#!/usr/bin/env ruby

require 'nlp_ruby'
require 'trollop'


# reference-length hack as in (Nakov et al., 2012)
def brevity_penalty hypothesis, reference, hack=0
  a = tokenize hypothesis; b = tokenize reference
  return 1.0 if a.size>=b.size
  return Math.exp(1.0 - ((b.size.to_f+hack)/a.size));
end

def per_sentence_bleu hypothesis, reference, n=4, hack=0
  h_ng = {}; r_ng = {}
  (1).upto(n) {|i| h_ng[i] = []; r_ng[i] = []}
  ngrams(hypothesis, n) {|i| h_ng[i.size] << i}
  ngrams(reference, n) {|i| r_ng[i.size] << i}
  m = [n, reference.split.size].min
  weight = 1.0/m
  add = 0.0
  sum = 0
  (1).upto(m) { |i|
    counts_clipped = 0
    counts_sum = h_ng[i].size
    h_ng[i].uniq.each {|j| counts_clipped += r_ng[i].count(j)}
    add = 1.0 if i >= 2
    sum += weight * Math.log((counts_clipped + add)/(counts_sum + add));
  }
  return brevity_penalty(hypothesis, reference, hack) * Math.exp(sum)
end

def main
  cfg = Trollop::options do
    opt :input, "input", :type => :string, :default => '-'
    opt :references, "references", :type => :string, :required => true
    opt :len_hack, "hack of Nakov et al", :type => :int, :default => 0
    opt :n, "N", :default => 4
  end

  refs = ReadFile.new(cfg[:references]).readlines_strip
  i = -1
  input = ReadFile.new cfg[:input]
  while line = input.gets
    i += 1
    if line.strip == ''
      puts 0.0
      next
    end
    puts per_sentence_bleu line.strip, refs[i], cfg[:n], cfg[:len_hack]
  end
  input.close
end


main